By pre-addition of photographically useful photographic reagents to photographic photosensitive materials, the effects which are realized are different from those observed when the reagents are included in a processing bath. The differences include, for example, the fact that photographic reagents which are liable to degradation by acids or alkalis, or under redox conditions, and which are unable to withstand long term storage in processing baths, can be used effectively. The processing bath composition can be simplified and adjustments can be made more easily, and it is possible for the required photographic reagents to act with the required timing, or in the required location. Thus the required photographic agents can be made to function in just a specified layer, or in the vicinity of a specified layer, in a multi-layer sensitive material, and the amount of the photographic reagent which is present can be varied as a function of silver halide development. However, if the photographic reagents are added to a photographic photosensitive material in an active form they may react with other components within the photographic photosensitive material during storage prior to processing, or they may be degraded by the effects of heat or oxygen, for example, and it may not be possible to realize the intended function at the time the material is processed. One way of overcoming this problem is to block the active group of the photographic reagent and to add the reagent to the photographic material in an essentially inactive form, which is to say as a photographic reagent precursor. In cases where the photographically useful reagent is a dye it is advantageous to block a functional group which has a major effect on the spectral absorbance of the dye and shifts the spectral absorbance to the short wavelength side or the long wavelength side so that there is no loss of photographic speed due to a filtering effect, even if it is included in the same layer as a silver halide emulsion which has a corresponding photosensitive spectral band. If the photographically useful reagent is an anti-foggant or a development inhibitor then it is possible to prevent an desensitizing action due to absorption on the photosensitive silver halide, or silver salt formation, during storage by blocking the active groups. By releasing these photographic reagents with the required timing there is an advantage that fogging can be prevented without loss of photographic speed; that over-development fogging can be prevented; and that development can be stopped at the required time. In cases where the photographically useful group is a developing agent, an auxiliary developing agent to a fogging agent, prevention of the occurrence of various photographically adverse effects due to the formation of semi-quinones or oxidized forms by aerial oxidation during storage can be prevented. Prevention of the formation of fogging nuclei during storage by preventing electron implantation in the silver halide can be achieved by blocking the active groups or adsorption groups, and this has the effect stabilizing processing.
The above mentioned active groups, functional groups and adsorption groups are referred to collectively as "active groups" herein.
The use of photographic reagent precursors as described above is a very effective means of improving the performance of photographic reagents but, on the other hand, these precursors must satisfy very rigorous requirements. That is to say, they must satisfy the conflicting requirements of remaining stable under storage conditions, and of permitting the diisociation of the blocking group with the required timing and the smooth and effective release of the photographic reagent during processing.
A number of techniques have been proposed in the past for resolving these problems.
Any of the known blocking groups can be used as blocking groups for photographic reagents. For example, use can be made of the acyl groups and sulfonyl groups disclosed in JP-B-48-9969, JP-A-52-8828, JP-A-57-82834, U.S. Pat. No. 3,311,476 and JP-B-47-44805 (U.S. Pat. No. 3,615,617), the blocking groups which release a photographically useful reagent by means of a reverse Michael reaction disclosed in JP-B-55-17369 (U.S. Pat. No. 3,888,677), JP-B-55-9696 (U.S. Pat. No. 3,791,830), JP-B-55-34927 (U.S. Pat. No. 4,009,029), JP-A-56-77842 (U.S. Pat. No. 4,307,175), JP-A-59-105642 and JP-A-59-105640, the blocking groups which release a photographically useful reagent with the formation of a quinonemethide or a quinonemethide-like compound by means of intramolecular electron transfer disclosed in JP-B-54-39727, U.S. Pat. Nos. 3,674,478, 3,932,480 and 3,993,661, JP-A-57-135944, JP-A-57-135945 and JP-A-57-136640, those in which an intramolecular ring closing reaction is used, disclosed in JP-A-55-53330 and JP-A-59-218439, those in which the ring opening of a five or six membered ring is used, disclosed in JP-A-76541 (U.S. Pat. No. 4,335,200), JP-A-57-135949, JP-A-57-179842, JP-A-59-137945, JP-A-59-140445, JP-A-59-219741 and JP-A-60-41034, the blocking groups which release photographically useful reagents by means of a Michael reaction disclosed in JP-A-59-201057, JP-A-61-43739, JP-A-61-95346 and JP-A-61-95347, and the blocking groups which release a photographically useful reagent as the development reaction of the silver halide proceeds, as disclosed in JP-A-60-233648, JP-A-61-156043 and JP-A-61-236549. (The term "JP-A" as used herein means an "unexamined published Japanese patent application", and the term "JP-B" as used herein means an "examined Japanese patent publication".)
However, the photographically useful reagents which have been blocked with these known blocking groups are either stable under storage conditions but have a photographic reagent release rate which is too low and require highly alkaline conditions of pH 12 or above, or they deteriorate gradually under storage conditions when the release rate in processing baths of pH 9 to 11 is satisfactory and lose their function as precursors, and since it is not possible to control the photographic reagent release rate to any extent there is a disadvantage in that the pH range which can be used is limited.